Wire coat compound containing esters of aminobenzoic acid

ABSTRACT

This invention relates to the discovery that esters of aminobenzoic acid, when used as a replacement in whole or in part of conventional cobalt materials, maintains the rubber-to-wire adhesion properties.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 4,513,121 discloses rubber skim stock containingorgano-cobalt compounds as adhesion promoters. Representative examplesof such organo-cobalt compounds include cobalt salts of fatty acids,cobalt salts of aliphatic or alicyclic carboxylic acids having from 6 to30 carbon atoms, cobalt chloride, cobalt naphthenate, cobalt carboxylateand organo-cobalt-boron complexes. Problems associated with suchorgano-cobalt compounds include its availability and strong pro-oxidantproperties which can adversely affect rubber by accelerating oxidation.

SUMMARY OF THE INVENTION

The present invention relates to a rubber composition particularlysuited as a wire coat stock containing esters of aminobenzoic acid.

DETAILED DESCRIPTION OF THE INVENTION

There is disclosed a wire coat compound comprising:

(a) a rubber selected from the group consisting of natural rubber and ablend of natural rubber and a synthetic rubber derived from a dienemonomer; and

(b) from about 0.1 to about 10 phr of an ester of aminobenzoic acid ofthe formula: ##STR1## wherein R is an alkyl radical having from 8 to 24carbon atoms; (c) from 0.1 to 10 phr of a methylene acceptor; and

(d) from 0.1 to 10 phr of a methylene donor.

The esters of aminobenzoic acid for use in the present invention are ofthe above formula I. Preferably, R is an alkyl radical having from 8 to24 carbon atoms. Representative examples of such esters include octylaminobenzoate, nonyl aminobenzoate, decyl aminobenzoate, undecylaminobenzoate, dodecyl aminobenzoate, tridecyl aminobenzoate, tetradecylaminobenzoate, pentadecyl aminobenzoate, hexadecyl aminobenzoate,heptadecyl aminobenzoate, octadecyl aminobenzoate, nonadecylaminobenzoate and eicosyl aminobenzoate.

Whereas the most common isomeric form of the above esters is, forexample, octadecyl-4-aminobenzoate, it is contemplated herein that the3-and even the 2- forms may be used. For ease of preparation and cost,the 4-isomeric form is preferred.

The above ester is present in the wire coat compound in a range of fromabout 0.1 to 10 phr. Preferably, the ester is present in an amountranging from about 0.5 to 2 phr.

The wire coat compound contains natural rubber. The natural rubberincludes its various forms, e.g., pale crepe and smoked sheet, andbalata and gutta percha. The rubber may be solely natural rubber or ablend of natural rubber and synthetic rubber. The synthetic polymers arederived from a diene monomer and include those prepared from a singlemonomer (homopolymer) or a mixture of two or more copolymerizablemonomers (copolymer) when the monomers are combined in the randomdistribution or block form. The monomers may be substituted orunsubstituted and may possess one or more double bonds, conjugated andnonconjugated dienes and monoolefins, including cyclic and acyclicmonoolefins, especially vinyl and vinylidene monomers. Examples ofconjugated dienes are 1,3-butadiene, isoprene, chloroprene,2-ethyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene and piperylene.Examples of nonconjugated dienes are 1,4-pentadiene, 1,4-hexadiene,1,5-hexadiene, dicyclopentadiene, 1,5-cyclooctadiene, and ethyldienenorbornene. Examples of acyclic monoolefins are ethylene, propylene,1-butene, isobutylene, 1-pentene and 1-hexene. Examples of cyclicmonoolefins are cyclopentene, cyclohexene, cycloheptene, cyclooctene and4-methyl-cyclooctene. Examples of vinyl monomers are styrene,acrylonitrile, acrylic acid, ethylacrylate, vinyl chloride,butylacrylate, methyl vinyl ether, vinyl acetate and vinyl pyridine.Examples of vinylidene monomers are alpha-methylstyrene, methacrylicacid, methyl methacrylate, itaconic acid, ethyl methacrylate, glycidylmethacrylate and vinylidene chloride. Representative examples of thesynthetic polymers used in the practice of this invention arepolychloroprene homopolymers of a conjugated 1,3-diene such as isopreneand butadiene, and in particular, polyisoprenes and polybutadieneshaving essentially all of their repeat units combined in acis-1,4-structure; and copolymers of a conjugated 1,3-diene such asisoprene and butadiene with up to 50 percent by weight of at least onecopolymerizable monomer, including ethylenically unsaturated monomerssuch as styrene or acrylonitrile; and butyl rubber, which is apolymerization product of a major proportion of a monoolefin and a minorproportion of a diolefin such as butadiene or isoprene. The rubber maybe emulsion polymerized or solution polymerized.

The preferred synthetic rubbers which may be used with the presentinvention are cis-1,4-polyisoprene, polybutadiene, polychloroprene andthe copolymers of isoprene and butadiene, copolymers of acrylonitrileand butadiene, copolymers of acrylonitrile and isoprene, copolymers ofstyrene, butadiene and isoprene, copolymers of styrene and butadiene andblends thereof. Since the compounds of the present invention are used asa wire coat composition, natural rubber is preferably present and mayeven be partially replaced with some synthetic rubber. When used as ablend, the natural rubber is preferably present in an amount rangingfrom 5 to 95 weight percent of the total rubber present in the wire coatcompound.

In-situ resins are formed in the wire coat stock and involve thereaction of a methylene acceptor and a methylene donor. The term"methylene donor" is intended to mean a compound capable of reactingwith a methylene acceptor and generate the resin in-situ. Examples ofmethylene donors which are suitable for use in the present inventioninclude hexamethylenetetramine, hexaethoxymethylmelamine,hexamethoxymethylmelamine, lauryloxymethylpyridinium chloride,ethoxymethylpyridinium chloride, trioxan hexamethoxymethylmelamine, thehydroxy groups of which may be esterified or partly esterified, andpolymers of formaldehyde such as paraformaldehyde. In addition, themethylene donors may be N-substituted oxymethylmelamines, of the generalformula: ##STR2## wherein X is an alkyl having from 1 to 8 carbon atoms,R¹ R², R³, R⁴ and R⁵ are individually selected from the group consistingof hydrogen, an alkyl having from 1 to 8 carbon atoms, the group --CH₂OX or their condensation products. Specific methylene donors includehexakis-(methoxymethyl)melamine, N,N',N"-trimethyl/N,N',N"-trimethylolmelamine, hexamethylolmelamine, N-methylolmelamine,N,N'-dimethylolmelamine, N,N',N"- tris(methoxymethyl)melamine andN,N'N"-tributyl-N,N',N"-trimethylol-melamine. The N-methylol derivativesof melamine are prepared by known methods.

The amount of methylene donor that is present in the rubber stock mayvary. Typically, the amount of methylene donor that is present willrange from about 0.1 phr to 10.0 phr. Preferably, the amount ofmethylene donor ranges from about 2.0 phr to 5.0 phr.

Examples of methylene acceptors include activated phenols by ringsubstitution and a cashew nut oil modified novalak-type phenolic resin.Representative examples of activated phenols by ring substitutioninclude resorcinol, cresols, t-butyl phenols, isopropyl phenols, ethylphenols and mixtures thereof. Cashew nut oil modified novolak-typephenolic resins are commercially available from Schenectady ChemicalsInc under the designation SP6700. The modification rate of oil based ontotal novolak-type phenolic resin may range from 10 to 50 percent. Forproduction of the novolak-type phenolic resin modified with cashew nutoil, various processes may be used. For example, phenols such as phenol,cresol and resorcinol may be reacted with aldehydes such asformaldehyde, paraformaldehyde and benzaldehyde using acid catalysts.Examples of acid catalysts include oxalic acid, hydrochloric acid,sulfuric acid and p-toluenesulfonic acid. After the catalytic reaction,the resin is modified with the oil.

The amount of methylene acceptor that is present in the rubber stock mayvary. Typically, the amount of methylene acceptor that is present willrange from about 0.1 phr to 10 phr. Preferably, the amount of methyleneacceptor ranges from about 2.0 phr to 5.0 phr.

As known to one skilled in the art, in order to cure a rubber stock, oneneeds to have a sulfur vulcanizing agent. Examples of suitable sulfurvulcanizing agents include elemental sulfur (free sulfur) or a sulfurdonating vulcanizing agent, for example, an amine disulfide, polymericpolysulfide or sulfur olefin adducts. Preferably, the sulfur vulcanizingagent is elemental sulfur in the insoluble form. The amount of sulfurvulcanizing agent will vary depending on the components of the rubberstock and the particular type of sulfur vulcanizing agent that is used.The sulfur vulcanizing agent is generally present in an amount rangingfrom about 0.5 to about 8 phr. Preferably, the sulfur vulcanizing agentis present in an amount ranging from about 0.75 phr to about 4.0 phr.

Conventional rubber additives may be incorporated in the rubber stock ofthe present invention. The additives commonly used in rubber stocksinclude fillers, plasticizers, waxes, processing oils, retarders,antiozonants, antioxidants and the like. The total amount of filler thatmay be used may range from about 30 to about 150 phr, with a range offrom about 45 to about 100 phr being preferred. Fillers include clays,calcium carbonate, calcium silicate, titanium dioxide and carbon black.Representatives carbon blacks that are commonly used in rubber stocksinclude N326, N330, N472, N630, N642, N660, N754, N762, N765 and N990.Plasticizers are conventionally used in amounts ranging from about 2 toabout 50 phr with a range of about 5 to about 30 phr being preferred.The amount of plasticizer used will depend upon the softening effectdesired. Examples of suitable plasticizers include aromatic extractoils, petroleum softeners including asphaltenes, pentachlorophenol,saturated and unsaturated hydrocarbons and nitrogen bases, coal tarproducts, cumarone-indene resins and esters such as dibutylphthalate andtricresol phosphate. Common waxes which may be used include paraffinicwaxes and microcrystalline blends. Such waxes are used in amountsranging from about 0.5 to 3 phr. Materials used in compounding whichfunction as an accelerator-activator includes metal oxides such as zincoxide and magnesium oxide which are used in conjunction with acidicmaterials such as fatty acid, for example, stearic acid, oleic acid andthe like. The amount of the metal oxide may range from about 1 to about14 phr with a range of from about 2 to about 8 phr being preferred. Theamount of fatty acid which may be used may range from about 0 phr toabout 5.0 phr with a range of from about 0 phr to about 2 phr beingpreferred.

Accelerators are used to control the time and/or temperature requiredfor vulcanization and to improve the properties of the vulcanizate. Inone embodiment, a single accelerator system may be used; i.e., primaryaccelerator. The primary accelerator(s) may be used in total amountsranging from about 0.5 to about 4, preferably about 0.8 to about 2.0,phr. In another embodiment, combinations of a primary and a secondaryaccelerator might be used with the secondary accelerator being used in asmaller, equal or greater amount to the primary accelerator.Combinations of these accelerators might be expected to produce asynergistic effect on the final properties and are somewhat better thanthose produced by use of either accelerator alone. In addition, delayedaction accelerators may be used which are not affected by normalprocessing temperatures but produce a satisfactory cure at ordinaryvulcanization temperatures. Vulcanization retarders might also be used.Suitable types of accelerators that may be used in the present inventionare amines, disulfides, guanidines, thioureas, thiazoles, thiurams,sulfenamides, dithiocarbamates and xanthates. Preferably, the primaryaccelerator is a sulfenamide. If a second accelerator is used, thesecondary accelerator is preferably a guanidine, dithiocarbamate orthiuram compound.

The rubber compounds of the present invention may also contain a cureactivator. A representative cure activator is methyl trialkyl (C₈ -C₁₀)ammonium chloride commercially available under the trademark Adogen® 464from Sherex Chemical Company of Dublin, Ohio. The amount of activatormay be used in a range of from 0.05 to 5 phr.

Siliceous pigments may be used in the rubber compound applications ofthe present invention, including pyrogenic and precipitated siliceouspigments (silica), although precipitate silicas are preferred. Thesiliceous pigments preferably employed in this invention areprecipitated silicas such as, for example, those obtained by theacidification of a soluble silicate, e.g., sodium silicate. Such silicasmight be characterized, for example, by having a BET surface area, asmeasured using nitrogen gas, preferably in the range of about 40 toabout 600, and more usually in a range of about 50 to about 300 squaremeters per gram. The BET method of measuring surface area is describedin the Journal of the American Chemical Society, Volume 60, page 304(1930). The silica may also be typically characterized by having adibutylphthalate (DBP) absorption value in a range of about 100 to about400, and more usually about 150 to about 300. The silica might beexpected to have an average ultimate particle size, for example, in therange of 0.01 to 0.05 micron as determined by the electron microscope,although the silica particles may be even smaller, or possibly larger,in size. Various commercially available silicas may be considered foruse in this invention such as, only for example herein, and withoutlimitation, silicas commercially available from PPG Industries under theHi-Sil trademark with designations 210, 243, etc; silicas available fromRhone-Poulenc, with, for example, designations of Z1165MP and Z165GR andsilicas available from Degussa AG with, for example, designations VN2and VN3, etc. Generally speaking, the amount of silica may range from 5to 120 phr. Since the intended use of the present invention is as a wirecoat compound, the silica will generally range from about 10 to 30 phr.

A class of compounding materials known as scorch retarders are commonlyused. Phthalic anhydride, salicylic acid, sodium acetate andN-cyclohexyl thiophthalimide are known retarders. Retarders aregenerally used in an amount ranging from about 0.1 to 0.5 phr.

Conventionally, antioxidants and sometimes antiozonants, hereinafterreferred to as antidegradants, are added to rubber stocks.Representative antidegradants include monophenols, bisphenols,thiobisphenols, polyphenols, hydroquinone derivatives, phosphites,thioesters, naphthyl amines, diphenyl-p-phenylenediamines,diphenylamines and other diaryl amine derivatives,para-phenylenediamines, quinolines and mixtures thereof. Specificexamples of such antidegradants are disclosed in The Vanderbilt RubberHandbook (1990), pages 282-286. Antidegradants are generally used inamounts from about 0.25 to about 5.0 phr with a range of from about 1.0to about 3.0 phr being preferred.

The rubber compound of the present invention is used as a wire coat orbead coat for use in a tire. In such instances, the ester ofaminobenzoic acid may be used as a replacement in whole or in part forcobalt materials. When it is desired to use the ester of aminobenzoicacid as a partial replacement, any of the cobalt materials known in theart to promote the adhesion of rubber to metal may be used. Thus,suitable cobalt materials which may be employed include cobalt salts offatty acids such as stearic, palmitic, oleic, linoleic and the like;cobalt salts of aliphatic or alicyclic carboxylic acids having from 6 to30 carbon atoms, such as cobalt neodecanoate; cobalt chloride, cobaltnaphthenate; cobalt carboxylate and an organo-cobalt-boron complexcommercially available under the designation Manobond C from Wyrough andLoser, Inc, Trenton, N. J. Manobond C is believed to have the structure:##STR3## in which R⁶ is an alkyl group having from 9 to 12 carbon atoms.

Amounts of organo-cobalt compound which may be employed depend upon thespecific nature of the cobalt material selected, particularly the amountof cobalt metal present in the compound.

The amount of the cobalt material may range from about 0.2 to 5 phr.Preferably, the amount of cobalt compound may range from about 0.5 to 2phr. When used, the amount of cobalt material present in the stockcomposition should be sufficient to provide from about 0.01 percent toabout 0.50 percent by weight of cobalt metal based upon total weight ofthe rubber stock composition with the preferred amounts being from about0.03 percent to about 0.2 percent by weight of cobalt metal based ontotal weight of skim stock composition.

The sulfur vulcanizable rubber compound is cured at a temperatureranging from about 125° C. to 180° C. Preferably, the temperature rangesfrom about 135° C. to 1600° C.

The mixing of the rubber compound can be accomplished by methods knownto those having skill in the rubber mixing art. For example, theingredients are typically mixed in at least two stages, namely at leastone non-productive stage followed by a productive mix stage. The finalcuratives are typically mixed in the final stage which is conventionallycalled the "productive" mix stage in which the mixing typically occursat a temperature, or ultimate temperature, lower than the mixtemperature(s) than the preceding non-productive mix stage(s). The esterof aminobenzoic acid and cobalt compound, if used, is mixed in one ormore non-productive mix stages. The sulfur and accelerator(s) aregenerally mixed in the productive mix stage. The terms "non-productive"and "productive" mix stages are well known to those having skill in therubber mixing art.

The rubber composition of this invention is directed to wire coat orbead coat compounds. For example, it can be used for wire coat in hose,belts and, in particular, tires. Such pneumatic tires can be built,shaped, molded and cured by various methods which are known and will bereadily apparent to those having skill in such art. As can beappreciated, the tire may be a passenger tire, aircraft tire, truck tireand the like.

The present invention may be better understood by reference to thefollowing examples in which the parts or percentages are by weightunless otherwise indicated.

EXAMPLE 1 Preparation of Octadecyl-4-Aminobenzoate

A 1-liter round bottom flask was fitted with a reflux condenser, DeanStark trap and heating mantle and charged with 54 g (0.20 mole) of1-octadecanol, 33 g (0.20 mole) ethyl 4-aminobenzoate, 8 g ofp-toluenesulfonic acid and 500 ml of mixed xylenes. The flask wasflushed with nitrogen and sealed under a nitrogen balloon. The reactionsystem was heated to reflux with a pot temperature of about 140° C. andallowed to reflux for about 1/2 hour before a 25 ml-aliquot ofxylenes-ethanol mixture was removed through the Dean-Stark trap. Every5-10 minutes, another 25 ml aliquot of the xylenes-ethanol mixture wasremoved until a total of 400 ml had been withdrawn from the reactionmixture and the pot attained a temperature of 150° C. Remainingvolatiles were removed under 29 inches of Hg vacuum at 70° C. in avacuum oven to give 95 g of an off-white waxy material melting at60°-70° C., with an infrared spectrum showing the amino-aromatic esterwith a long-chain aliphatic tail.

EXAMPLE 2

Each rubber stock was prepared in a two non-productive, one productiveBanbury mix procedure. Other than the ingredients listed in Table I, thenonproductive stages for both samples contained synthetic polyisoprene,natural rubber, resorcinol, cobalt compound (if used),octadecyl-4-aminobenzoate (if used) and conventional amounts ofprocessing oil, stearic acid, zinc oxide, carbon black, antidegradantsand silica. The hexamethoxymelamine along with convention amounts ofaccelerators, antidegradant, zinc oxide and sulfur were added during theproductive stage. Table I below shows the levels of rubber, cobaltcompound, resorcinol, hexamethoxymelamine and octadecyl-4-aminobenzoatewhich was used. All parts and percentages are by weight unless otherwisenoted.

                  TABLE I                                                         ______________________________________                                                       Con-   Con-                                                                   trol   trol                                                    Sample         1      2      3    4    5    6                                 ______________________________________                                        Synthetic Polyisoprene.sup.1                                                                 25     25     25   25   25   25                                Natural Rubber 75     75     75   75   75   75                                Cobalt Naphthenate                                                                           1.0    0.50   .50  0.5  0    0                                 Octadecyl-4-Aminobenzoate                                                                    0      0      .50  1.0  .50  1.0                               Resorcinol     4      4      4    4    4    4                                 Hexamethoxymelamine                                                                          3      3      3    3    3    3                                 ______________________________________                                         .sup.1 Solution polymerized polyisoprene commercially available from The      Goodyear Tire & Rubber Company under the trademark description Natsyn         ® 2200.                                                              

Cure properties were determined using a Monsanto oscillating discrheometer which was operated at a temperature of 150° C. and 100 cyclesper minute. A description of oscillating disc rheometers can be found inthe Vanderbilt Rubber Handbook edited by Robert O. Ohm (Norwalk, Conn.,R. T. Vanderbilt Company, Inc., 1990), pages 554-557. The use of thiscure meter and standardized values read from the curve are specified inASTM D-2084. A typical cure curve obtained on an oscillating discrheometer is shown on page 555 of the 1990 edition of the VanderbiltRubber Handbook.

In such an oscillating disc rheometer, compounded rubber samples aresubjected to an oscillating shearing action of constant amplitude. Thetorque of the oscillating disc embedded in the stock that is beingtested that is required to oscillate the rotor at the vulcanizationtemperature is measured. The values obtained using this cure test arevery significant since changes in the rubber or the compounding recipeare very readily detected. It is obvious that it is normallyadvantageous to have a fast cure rate.

The following Table II reports cure properties that were determined fromcure curves that were obtained for the rubber stocks that were prepared.These properties include a torque minimum (Min. Torque), a torquemaximum (Max. Torque), minutes to 25 percent of the torque increase(t25) and minutes to 90 percent of the torque increase (t90).

Strebler adhesion testing was done to determine the interfacial adhesionbetween the rubber formulations that were prepared. The interfacialadhesion was determined by pulling one compound from another at a rightangle to the untorn test specimen with the two right ends being pulledapart at a 1800° angle to each other using an Instron machine. The areaof contact was determined from placement of a Mylar® sheet between thecompounds during cure. A window in the Mylar® allowed the materials tocome into contact with each other during testing.

Standard wire adhesion tests (SWAT) were conducted by embedding a singlebrass-plated cord in the respective rubber compositions. The rubberarticles were then cured at 150° C. for 28 minutes. The steel cord inthese rubber compositions were then subjected to a pull-out test,according to ASTM Standard D2229-73. The results of these pull-out tests(SWAT) are given below and identified as Original in Table II andexpressed in Newtons. Adhesion tests were also conducted on the rubberarticles after curing and then subjecting the cured samples to (1) 5days in water at 90° C., (2) 10 days in water at 90° C. and (3) 10 daysat 90° relative humidity at 75° C.

                  TABLE II                                                        ______________________________________                                                     Control Control                                                  Sample       1       2       3    4    5    6                                 ______________________________________                                        Cobalt Naphthenate (phr)                                                                   1.0     0.5     .50  .5   0    0                                 Ester of Example 1                                                                         0       0       .50  1.0  .50  1.0                               Rheometer Cure at                                                             150° C.                                                                Min Torque   7.1     7.8     8.0  8.2  .7.8 7.8                               Max Torque   61.7    58.9    62.1 61.4 63.2 61.9                              T25 (min)    6.3     6.3     6.0  5.9  5.9  5.9                               T90 (min)    16.7    17.3    16.6 16.4 16.2 16.3                              Cured Properties                                                              300% Modulus (MPa)                                                                         13.9    12.8    13.9 13.5 14.1 13.5                              Tensile @ Break (MPa)                                                                      18.4    18.9    18.8 18.8 18.7 18.0                              Elongation @ Break (%)                                                                     430     460     430  450  422  440                               Rebound @ RT 40.8    41.7    42.3 42.1 42.1 42                                Rebound @ 100° C.                                                                   56.2    56.6    57.6 57.7 57.3 57.5                              Hardness @ RT                                                                              80.8    77.8    80.6 79.0 80   78.1                              Hardness @ 100° C.                                                                  76      73.8    76.3 75.5 75.8 74.4                              Strebler Adhesion @                                                                        44      77      42   47   46   43                                95° C. to Self                                                         Monsanto Fatigue to                                                                        500     652     604  703  545  500                               Failure (cycles)                                                              SWAT (Newtons)                                                                Original     615     621     652  622  652  625                               Aged (75° C. 10                                                                     720     700     730  711  740  730                               days in 90° RH)                                                        Aged (90° C. 5                                                                      652     600     650  600  636  630                               days in water)                                                                Aged (90° C. 10                                                                     420     431     430  431  451  416                               days in water)                                                                ______________________________________                                    

Table II shows that the total or partial replacement of cobalt with thelong-chain ester of 4-aminobenzoic acid maintains the state of cure ofthe rubber, the stress-strain properties, rebound and hardness andStrebler adhesion of the rubber to itself at 1.0 phr cobalt. Thefatigue-to-failure cycles is also maintained or exceeded with cobaltreplacement.

The original and aged SWAT adhesion of the wire coat compoundscontaining a partial or total replacement of cobalt material with thelong chain ester of 4-aminobenzoic acid was most importantly maintainedto the controls, after aging.

What is claimed is:
 1. A wire coat compound comprising:(a) a rubberselected from the group consisting of natural rubber and blends ofnatural rubber and a synthetic rubber derived from a diene monomer; (b)from about 0.1 to about 10 phr of an ester of aminobenzoic acid of theformula: ##STR4## wherein R is an alkyl radical having from 8 to 24carbon atoms; (c) from 0.1 to 10 phr of a methylene acceptor; and (d)from 0.1 to 10 phr of a methylene donor.
 2. The compound of claim 1wherein said rubber is natural rubber.
 3. The compound of claim 1wherein said rubber is a blend of natural rubber and a synthetic rubberselected from the group consisting of cis-1,4-polyisoprene,polybutadiene, copolymers of isoprene and butadiene, copolymers ofacrylonitrile and butadiene, copolymers of styrene, butadiene andisoprene, copolymers of styrene and butadiene and blends thereof.
 4. Thecompound of claim 1 wherein said rubber comprises a blend of naturalrubber and a synthetic rubber and said natural rubber is present in anamount ranging from 5 to 95 weight percent of the total rubber presentin the compound.
 5. The compound of claim 1 wherein R is an alkylradical having from 8 to 24 carbon atoms.
 6. The compound of claim 1wherein said ester of aminobenzoic acid is present in an amount rangingfrom 0.5 to 2 phr.
 7. The compound of claim 1 wherein said methylenedonor is selected from the group consisting of hexamethylenetetramine,hexaethoxymethylmelamine, hexamethoxymethylmelamine,lauryloxymethylpyridinium chloride, ethoxymethylpyridinium chloride,trioxan hexamethoxymethylmelamine polymers of formaldehyde,hexakis-(methoxymethyl)melamine,N,N',N"-trimethyl/N,N',N"-trimethylolmelamine, hexamethylolmelamine,N-methylolmelamine, N,N'-dimethylolmelamine,N,N',N"-tris(methoxymethyl)melamine and N,N'N"-tributyl-N,N',N"-trimethylol-melamine.
 8. The compound of claim 1 wherein saidmethylene acceptor is selected from the group consisting of activatedphenols by ring substitution and cashew nut oil modified novalak-typephenolic resin.
 9. The compound of claim 8 wherein said activated phenolis selected from the group consisting of resorcinol, cresols, t-butylphenols, isopropyl phenols, ukyl phenols and mixtures thereof.
 10. Therubber compound of claim 1 additionally containing a cobalt compound.11. The rubber compound of claim 10 wherein said cobalt compound ispresent in an amount ranging from 0.2 to 5 phr.
 12. The rubber compoundof claim 10 wherein said cobalt compound is selected from the groupconsisting of cobalt salts of fatty acids, cobalt salts of aliphatic oralicyclic carboxylic acids having from 6 to 30 carbon atoms, cobaltchloride, cobalt naphthenate, cobalt carboxylate and organocobalt-boroncomplexes.
 13. The rubber compound of claim 12 wherein said cobaltcompound is selected from the group consisting of cobalt neodecanoateand cobalt naphthenate.
 14. A pneumatic tire having a wire coatcomprising the compound of claim
 1. 15. A pneumatic tire having a beadcoat comprising the compound of claim 1.